1. Field of the invention
The present invention relates to a developing apparatus in electrophotographic coping machines. More particularly, it relates to a developing apparatus in which a doctor blade faces the surface of a developing sleeve with a given space therebetween.
2. Description of the prior art
In a dry developing method for electrophotography, it is necessary to accurately form a uniform toner layer on an electrostatic latent image on the surface of the photosensitive drum, in order to obtain a satisfactory visible image. One method by which the amount of toner that reaches the surface of the photosensitive drum can be controlled is to establish a fixed distance between the surface of a developing sleeve, which transfers the toner to the surface of the photosensitive drum from the vicinity of the drum, and a doctor blade. This distance must be established with high precision within the limits of approximately .+-.50 .mu.. With conventional blades, attachment is by means of adjustment screws, etc., to the side walls of a developer housing. A device such as a thickness gauge is used for both measurement and adjustment of the fixed distance to within the very narrow limits. However, depending upon the pressure with and /or the angle at which this gauge is placed in the space between the sleeve and the blade, the distance is changed, so that a space of varying dimensions (between, for example, the ends of the blade and its center) may result between the blade and the sleeve. Also, individual difference in factors such as skillfulness between one measurer and another may result in differences in this space.
For example, when pieces of dust or similar kinds of foreign matter are mixed into the toner, the foreign matter may form lumps in the space between the sleeve and the blade. The result is that areas upon which the toner does not settle occur in stripes on the sleeve. Therefore, it is necessary to eliminate the foreign matter that has formed lumps in the space by removing the blade at regular intervals. When the space is once again adjusted, then, for the reasons stated above, the reproducibility is poor, which is undesirable.
If the adjustment of the space is not properly done, then a uniform amount of the toner cannot be distributed over the surface of the photosensitive drum, resulting in the final image with irregularities and/or a high fog density.